Hey all, first post here although I think Wiisass has had input on another of my projects over at www.hybridz.org, when I was relocating the steering rack and making new tie rod ends for bumpsteer adjustment.

What I'm looking for is some strut information. I have a 240Z which is being built for autoxing and track days. I am planning to run some very stiff spring rates. Most Z guys stick to the ~200 to 350 in/lb spring rates, I am going to be running in the 500 to 600 in/lb range I think. A few guys (mostly in OR) have really been upping the rates and seeing very good results. The struts commonly available (Tokico, KYB, etc) are just not suitable for this kind of rate, probably because the chassis itself isn't stiff enough to support these stiff springs in stock form, so the chassis effectively becomes the spring. I have installed a fairly thorough cage which should provide the stiffness needed to cope with the spring rates I'm planning.

In looking I've narrowed my search down to just a couple options. I'm curious about the Koni 8611-1257RACE - double adjustable units vs the VW Bilsteins, P30-0032. There has been some talk on Hybrid Z about failure of the top strut bushing in the Konis, although I don't think I've seen reports of this anywhere else. The same guy reporting the issues with the Konis raves about the Bilsteins, specifically after having them revalved "300/100". The Bilsteins are about half the price of the Konis after revalving is factored in, and are non-adjustable. This guy also prepped cars that have won the ARRC, so presumably he knows his shit.

From a technical perspective I seem to think that the larger shaft and correspondingly larger bushing on the Bilstein would reduce stiction in the suspension. From a non-technical perspective, I've had really good results with Bilsteins in the past, so I have a warm fuzzy feeling about them in general.

So the questions I have are:
1. How can I tell what spring rates the two struts can actually cope with?
I really don't have enough experience reading shock dyno graphs to understand what I'm looking at. I do know the weight of the car will be in the 2100 to 2200 lb range and corner weights should be no less than ~475 lbs to no more than 605 lbs. Wheel rate on the Z is .98 of spring rate.
2. How big a deal is being able to adjust the strut?
It seems to me that once you get the damping dialed, there wouldn't be much of a need to change it. Maybe if the car was being run in the rain, but I'm probably not going to be doing that much if at all.
3. What does the 300/100 mean? I realize that the larger number probably corresponds to rebound valving and 100 corresponds to bump valving, but are these just plain percentages or are they aperture sizes in the washer stacks or what? The guy who suggested this was running spring rates in the 3-400 in/lb range, so if I'm going to 5-600 would the same numbers apply to me?
4. How hard is it to properly adjust the shocks, assuming I buy the DA Konis?
I've read Koni's instructions on how to adjust them but they seem relatively vague, and I'm wondering if I might be better off buying something that doesn't need messing with, vs buying something that I can screw up.
5. I'm thoroughly confused as to how one figures out what "optimally" damped suspension is, and whether that can be discerned from the spring rate vs shock dyno vs wheel rate or what. Is there a way to figure that out, or is it strictly test and tune? 6. It appears that the struts I'm choosing from are VW Rabbit inserts. Is there another Rabbit strut insert that I should be considering?

I'm not made of money and so whatever shock/spring upgrade I do is probably going to have to be lived with for several years at least, I'm just trying to make the most informed decision that I can. I know there are other options, such as Ground Control's AD ($400 per corner) and Penske (up to $2000 per corner) struts, but I just can't afford either of those options at this time. I'm looking to keep it at $250/corner or less for the struts.

Just a quick reply: I'm running 8611-1257's up front on my 240sx. They're set to about 1/3 for both bound and rebound with 600lb springs. You'll be fine with those for the rates you're looking at.

As for setting them, I basically guessed the initial settings and went by feel from there. I'm hoping to do more test & tuning with them in the future, though. I'm also using a MaxQ200 datalogger for now (belongs to a friend).

With just a quick run of the numbers the spring rates at least look good based on natural frequencies. I don't know about roll rates or anything because I don't have enough information.

I only have limited experience with the 8611. I helped some friends set up a race SRT4 that was running these at all 4 corners. But I was also able to get dyno plots from Koni that showed at least some of the adjustment. On that car, the front springs were 650lb/in and they were pretty much at the limit of where I would want the dampers. On the full stiff setting both compression and rebound were at critical in the low speed. But they also had different masses and were a good bit heavier than the Z.

But I have heard some issues with the Koni's, nothing that really can't be accounted for if you know about it. Supposedly the adjusters are non-linear, so a turn or a click at one end isn't going to be the same as a turn or a click at the other end of the adjustment range. I also don't really like the fact that they're twin tube. I mean they should be fine and can still perform, but I've never seen a true dyno plot for these and I would expect them to have some issues when seeing higher shock speeds or getting too hot. But a lot of people seem to run them without problems. Oh and the koni's seem to ride a little stiffer than I would like. But I don't know if it's at the point where it's hurting grip just making the driver a little uncomfortable.

By the way, what's the front/rear weight split on the Z or at least a close estimate?

As for the Bilsteins. I'm a big fan of Bilstein. I have had good experience with their stuff that they mean for people to take apart. And so far things are looking pretty promising with taking apart the stuff that they don't want people to take apart. I'll be putting up a thread with some of that information later today.

The inverted monotube strut inserts are nice pieces and if revalved properly, they would be very good dampers. You mention a 300/100 valving. That's Bilstein's notation for 3000N at 0.52m/s in rebound and 1000N at 0.52m/s in compression. I need to run some more numbers to tell you what that would actually mean for your car. But that's how they rate their linear valving. Which assuming that it is actually linear, you will end up having too many tradeoffs in the valving and either have too stiff of a ride or not enough compression damping for the low shock speed manuevers.

I really like their digressive pistons and valving. Besides a little problem of having a slightly progressive curve in the low-speed region, I was able to get a very stiff low speed section, but still keep the ride soft enough to not upset the tires or the driver. But I don't know what's available for the 30mm piston that the VW struts come with. Do you have any dimensions on the desired size of the strut. It might be possible to run a 36mm piston strut insert. There are a couple available out there and it's what I am currently working on.

As for your questions.

1. Based off of dyno plots and a whole slew of numbers and calculations along with the desired intent of the setup will give you some idea of how the dampers will perform with the given spring rates. If you can give me a couple more numbers, like estimates on unsprung weight, sway bar rates and installtion ratios and estimates on CG and roll center heights, I could do a quick work up of the car to get a better idea of what you're looking at.

2. It's not a big deal if they're valved properly. This means both numerically and to suit the track/car/driver to some extent. I'm a believer in making the tires happy before making the driver happy. I think it's better to make the driver adapt to the car and the car be faster than to hinder the performance of the car so the driver can feel faster.

So having adjustability can be nice, but it's only as good as the adjuster design and the person who's doing the adjusting. I would rather run a properly valved non-adjustable damper than a 4-way adjustable black box of a damper.

3. I explained this above. It's how Bilstein rates their linear dampers.

4. It's going to take a little time. without having a full printout of the dyno sheets for every adjustment range on the damper, you're going to have to just start soft and work your way up. There are a couple different ways to do it, everyone has their own style. I would just start with them all the way soft and then adjust based on what the car is doing. But only make one adjustment at a time. If you have better numbers for the dampers, you can make a guess of where you need to be and make adjustments from there. But the main part is when driving the car, you really need to feel where the problems are coming from.

5. There are ways to figure it out. From simple calculations to huge spreadsheets to full vehicle dynamics software packages. But even with all of that, there are still variables and assumptions that must be made and verified in physical testing.

6. I have no idea.

I hope this helps or at least gives you some idea.

Tim_________________TIP Engineering
Just put the TIP in.
R&D, damper development and fabrication.

with my 200 lb ass in the seat. I've lost ~20 lbs, I think the car will lose at least 200, maybe (hoping) closer to 300, so I figure the car should weigh somewhere between 2250 and 2350 roughly. I think I'll have added more weight to the rear with the cage additions and the removal of the dash, but I doubt it will be more rear biased than say 48/52.

So the Bilsteins are valved linear... that's a bummer. Seems like that's 10 year old technology. It sounds like it might be possible to have them valved digressive though... that would be better. The size of the necessary strut insert would be roughly 13" long x 1.795" or so in diameter. I don't know the exact diameter because there is a lip down inside the tube that my caliper wouldn't reach to, but that should be close. I can tell you that the Konis should be about the exact diameter. Pretty common for people installing them in a Z to need to remove the paint, they're that tight. So if you know the Koni's dimensions, that's the MAX...

I don't know the bar rates, but I think the install ratios will be pretty close to 1:1 because I set them up to be level with the control arms at ride height (I think that's what installation ratio means ???). I did modify them for minimal stiction and also made them adjustable. That project documented here: http://forums.hybridz.org/showthread.php?t=105596

I've never taken the time to calculate cg or measured unsprung weight so I've got a thread in on Hybrid Z to see if someone has a number I might extrapolate from.

I'll have adjustable front roll center, but the more I think about it with the spring rates I'm planning on running the more I think the roll center might be at or just above ground. I was previously planning on running my old soft springs and had planned on jacking up the RC height to prevent roll. I haven't calculated the rear roll center, but I'd guess 3-4 inches above ground.

Cg height should be in the 13-14 inch range as far as I can tell. I may try to get out and check the bar rates. They're solid bars, 1" in front and 3/4" in back, but I guess that doesn't tell you the length of the lever arms. Not really sure how to check the rates with the tools I have other than bolting the bar to a table and flexing one end 1 inch while standing on a bathroom scale, then watching the weight change... maybe I'll give that a shot.

I had to try a couple different methods to get the swaybar figures. What I ended up doing was bolting the bar mounts to some square stock and clamp that to my workbench. Then I attached the end link to another piece of square stock and set that on a bathroom scale. Then I took a piece of pipe, put it over the free end of the bar and moved it down one inch at the appropriate end link hole and read the scale on the other side to get the bar rates.

What I came up with was that the front bar has a min rate of about 105 lbs/in and a max rate of 120 lbs/in. The rear had a min rate of 50 lbs/in and a max of 80 lbs/in.

Jon, that sounds like it could work for the sway bars. The way I measure them is similar. I have a two mounts that I clamp to the work bench and mount the bar on. Then I fix one end of the bar and hang a known weight from the other end and measure the deflection. Except I measure the angles and then measure the moment arm and get a torsional stiffness for the bar itself. It's just a different way of doing what you did except my way is how I have all my calculations set up. It allows for a change in moment arm length to affect the roll rate from the sway bar. Which doesn't matter for stock or non-adjustable bars, but it is a lot easier for any type of adjustable bar. It means one measurement rather than however many adjustments there are.

But for the installation ratio of the sway bar. It's the same idea as the installation ratio for the shock and spring. It's how much the point where the endlink attahces to the lower control arm moves when the wheel center moves one inch. A good way to get a quick estimate of this is to measure the distance from the inner pivot to the endlink mount and then from the inner pivot to the lower ball joint. While this isn't the best way, it's a good quick way to get an idea of the movement of the sway bar.

You had mentioned that the sway bar installation ratio was 1:1, but that doesn't sound right, at least it doesn't if I'm remembering the S30 geometry correctly. If you could measure the way I said above, that would give a better idea.

Once I have that, I should have all the info I need to run a decent analysis. But do you have track and wheelbase dimensions. I could probably find them, but if you have them on hand it would be a lot easier.

As for the linear valving, it can work, but there are tradeoffs. Usually it's too soft of a compression side in order to keep the ride quality better. But digressive would be the way to go. I wonder if there would be an easy, meaning not incredibly difficult, way to get a bigger strut insert in the front. The strut tube is incorporated into the spindle on that car right? It makes things a little harder to do, but I'm sure something could be done. You should be fine with the koni's or the 30mm bilsteins, but it would nice to be able to have the 36mm piston. Or at least I think it would, that might change depending on how my other work goes for the 240sx. I might end up hating the 36mm setup by the time I get that all done. But if I don't, I should have a way to make it easily rebuildable/revalveable and it could end up making it easier for you.

Tim_________________TIP Engineering
Just put the TIP in.
R&D, damper development and fabrication.

I misunderstood installation ratio then. I know bars can be progressive or digressive based on the angle of the end link vs the angle of the control arm. I have mine set perpendicular to each other at ride height.

I got you some measurements for the distances from the inner pivot to the swaybar pivot and ball joint.
Front ball joint to inner control arm pivot = 12"
Front end link to inner control arm pivot = 8 1/4"
Rear inner to outer control arm pivot = 14 1/2"
Rear inner pivot to end link = 9 5/8"

Last edited by jmortensen on Tue Aug 14, 2007 6:25 pm; edited 1 time in total

Wheelbase is 90.5 and track width is 54.75. Might end up with a narrower track in the rear. Depends on how much tire I can fit back there.

EDIT-The spindle is integrated in the Z strut. There are workarounds, such as welding an internally threaded tube to the spindle and then running an externally threaded coilover, but I'm not quite ready to go that far at this point.

I've been thinking about the sway bar rates. I think they're 1/2 of what they should be, because I measured the pressure exerted on the far end of the bar and did not measure the pressure exerted with the pipe on the other end. Does that sound right?

Jon, the numbers look good, I just haven't had a chance to run them yet. There's been a million things going on. But I haven't forgotten about them, hopefully by the end of the week I will have something for you.

Tim_________________TIP Engineering
Just put the TIP in.
R&D, damper development and fabrication.

But I have heard some issues with the Koni's, nothing that really can't be accounted for if you know about it. Supposedly the adjusters are non-linear, so a turn or a click at one end isn't going to be the same as a turn or a click at the other end of the adjustment range. I also don't really like the fact that they're twin tube. I mean they should be fine and can still perform, but I've never seen a true dyno plot for these and I would expect them to have some issues when seeing higher shock speeds or getting too hot. But a lot of people seem to run them without problems. Oh and the koni's seem to ride a little stiffer than I would like. But I don't know if it's at the point where it's hurting grip just making the driver a little uncomfortable.

I have no answers to the questions asked here, but I thought I can contribute to what Wiisass was wondering.

I have dynoed some Koni shocks in the past.
One set I've dynoed was a classic Koni shock (dual adjustable) rebuilt by Truechoice. It came off of Vic Edelbrock's, a 196X Bud Moore's Mustang GT350. I believe the shocks were on there when Bud Moore was racing it. The other set was a Koni strut insert for a late model GTO and a rear shock for the same GTO.

Things to note about Koni's:
The DA Koni adjustments were real and apparent, unlike many adjustable shocks.

Full soft in one Koni does not yield same damping rates as the next (same P/N) shock. It varies significantly.

The GTO shock adjustments were real and apparent as well for both the insert and the rear shock.

The Koni twin tubes naturally cavitated.

The GTO front strut insert adjustments were not linear, though it was not as drastic as some seem to believe in the internet. However, when benchmarking the adjustment feature, the mechanism exhibited wierd behavior. Sweeping from full soft to full stiff, it would soften at a certain setting before it started stiffening up again.

There was minimal crosstalk between the compression adjustments and rebound adjustments.

I can post results of CVP and PVP upon request.

Tim, If I am doing too much of a threadjacking, please feel free to move it anywhere you like, just let me know where I can post results.

What I'm getting out of this is that the Konis have significant variances from unit to unit. I guess this means it would be a good idea to have a set of 4 matched so not only are they more expensive, they'd need rebuilding before even using them to get a properly functioning "set". Also the cavitation issue doesn't sound good, which really leads me back to the Bilsteins as the solution.

Post up everything you have. If you need space to host pictures or files, I can arrange that. For pictures, you should be able to just go to the gallery on here and create an account and then you can post up whatever pics you have. CVP plots only please, I'm not a fan of PVP plots, they're only good if that's all that's available.

One thing I'm interested in, is how far off the damping is out of the box and where. Is it a magnitude thing or slightly different curves or different knee? Could it be compensated with the adjusters and the knowledge of the individual shock plots? And at what test speeds did the caviation start to occur or was it present during even low speed damper testing?

And don't worry about threadjacking, it goes along well enough with the thread.

Tim_________________TIP Engineering
Just put the TIP in.
R&D, damper development and fabrication.

ost up everything you have. If you need space to host pictures or files, I can arrange that. For pictures, you should be able to just go to the gallery on here and create an account and then you can post up whatever pics you have. CVP plots only please, I'm not a fan of PVP plots, they're only good if that's all that's available.

One thing I'm interested in, is how far off the damping is out of the box and where. Is it a magnitude thing or slightly different curves or different knee? Could it be compensated with the adjusters and the knowledge of the individual shock plots? And at what test speeds did the caviation start to occur or was it present during even low speed damper testing?

And don't worry about threadjacking, it goes along well enough with the thread.

Tim

Tim,
Since I did the test with the Roehrig personally, I can generate all the plots in CVP form.

From the Koni's I've tested, the Bud Moore's race car (Mustang GT350) shocks were the ones that varied from one and another. The GTO ones were single units I tested. Note that the Bud Moore shocks were rebuilt by Truechoice once or more in their lifetime since production. From what I remember (it's been more than a year ago), the magnitude of the damping was different everywhere across the board. The difference between two shocks were able to be tuned out.

I dont recall at what speeds the Konis were cavitating at. I know it was at the compression stroke, but dont recall if it was occurring at maximum velocity or zero velocity.

When I get back to the office, I'll go see about getting some CVPs printed in jpeg form.

Jon, I will try and get to the numbers this weekend, I have just been real busy with a lot of other stuff here and haven't had time to get to it. But I will figure out what you can get away with and then we can figure out what a good setup will be.

Dennis, I saw that you were able to upload some plots onto the gallery. I didn't get a chance to look at them though, I just had noticed they were there the other day. But I plan on looking over them the next time I have the chance.

Tim_________________TIP Engineering
Just put the TIP in.
R&D, damper development and fabrication.

Just thought I'd follow up here. The following is clipped from another forum, but I think you'll get the idea.

I've been dealing with Chris Billings from the Shock Shop www.shock-shop.com and he was telling me that what he would prescribe for my situation would be very close to linear anyway, perhaps even PROgressive on the bump valving. He said it is possible to valve the Bilsteins to be slightly digressive or progressive, but with those pistons they're not going to have the sharp knee like a Koni or something that was designed digressive.

Chris would be a good source for purchasing the struts, as would www.shox.com, and he has some very interesting things to say about valving and spring rates. Basically what I got out of it is that we are using too much shock to compensate for not enough spring. When you get enough spring, then the shock valving can be reduced even though the spring rate goes up, and what this gives you at the wheel is a tire which stays more loaded all the time, because the rebound valving in particular isn't as stiff. Stiff rebound valving pulls the tire off the ground. He also says people valve the shocks to deal with the sprung weight, but they should be valving to handle the unsprung weight, since keeping the tire on the road is the goal. So he sacrifices ride quality for the ability to keep the load on the tire.

I'm going to try some struts revalved as he suggested with some pretty stiff spring rates (he charges $50 per corner for this service, so $100 for a roadracing Z since we only have front and rear valving, not usually left front/right front left rear/right rear). We'll find out how it all works out in 2025 when I get the car back on the road. He usually does road racing struts, so he wasn't sure exactly how the struts would work out for my application. What I'm doing is a pretty radical departure from what is "normal", so it may be that I'm heading down the wrong path, but if that is the case it's $65 per strut to fix it and I was willing to test his theory. Chris has a pretty good track record (he set up the shock/spring rates for the 4th place DSR car in last year's runoffs), but I guess I won't know for sure until I try.